1. Technical Field
This invention relates to heating, ventilation, and air conditioning (HVAC) systems. More specifically, the invention relates to a demand ventilation module.
2. Background Art
In an effort to provide maximum energy savings, many buildings are designed to be as airtight as possible. This is generally accomplished by limiting the amount of outside air infiltration. However, it has since been discovered that this tight building construction contributes significantly to the excessive build up of indoor air contaminants from various sources. These contaminants affect the health of building occupants resulting in what has become known as Sick Building Syndrome (SBS).
Various scientific studies concluded that buildings should be ventilated with a specific amount of outside air, based on occupancy and potential pollutant levels in the space, in order to allow the concentrations of indoor air pollutants to be reduced to acceptable levels. To this end, the American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) has established outdoor air standards that are usually adopted by most building codes and design engineers. Specifically, ASHRAE recommends ventilating buildings with different volumes of outside air based on a number of factors including potential pollutant levels and duration of occupant exposure encountered in specific applications.
To facilitate proper ventilation, previous strategies and products have been provided. A fixed air strategy has been provided to allow a fixed amount of outside air to infiltrate the building at all times through the HVAC system. This solution, however, results in excessive waste of energy when the room is not occupied and often overloads the HVAC system""s capacity to regulate thermal comfort. In addition, the HVAC blower must run continuously to provide continuous ventilation. Furthermore, conventional room thermostats have only two fan options: xe2x80x9cautoxe2x80x9d and xe2x80x9conxe2x80x9d. Both options are selected manually via a switch on the thermostat. When in the xe2x80x9cautoxe2x80x9d position, the fan cycles on and off with the heating or cooling demand. This means the HVAC fan and associated ventilation stop when the heating or cooling demand is satisfied. But when the fan selector is xe2x80x9conxe2x80x9d, then the room is constantly ventilated, even when unoccupied. Thus, the fixed air strategy wastes energy and adds more heating or cooling load to the HVAC system.
One present control strategy regulates the amount of outside air infiltration based on xe2x80x9cprojectedxe2x80x9d occupancy. The concept of this strategy is to reduce unnecessary ventilation by estimating when the room is either not full or unoccupied. This control strategy requires someone to xe2x80x9cprojectxe2x80x9d or estimate expected occupancy levels and physically manipulate the control set point. This strategy often results in over-ventilating or under-ventilating the space when estimates are inaccurate.
Energy Recovery Ventilators have also been designed to force outgoing room air and incoming outside air to pass through an air-to-air heat exchanger before entering the air conditioning system. The idea of these products is to transfer heat from one air source (the room) to another (outside air) in order to reduce load on the HVAC system. These products operate constantly, whether the room is occupied or not, adding load to the system (over-ventilating) at times when the space is not fully occupied or unoccupied altogether. Additionally, there is no provision to control the HVAC fan operation.
A preferred strategy is known as xe2x80x9cdemand ventilationxe2x80x9d. This concept involves regulating ventilation dampers to provide the minimum required amount of outside air based on actual demand.
Accordingly, what is needed is a ventilation apparatus that overcomes the drawbacks of previous ventilation strategies and products, such as energy waste, increased heating or cooling load, increased maintenance and electrical consumption, noise, and the lack of HVAC operation control, through a demand ventilation module that regulates ventilation in direct proportion to actual occupancy of an inside space automatically. The invention solves these ventilation problems of previous strategies and products through a retrofit demand ventilation module for use with HVAC systems to facilitate compliance with ventilation requirements for acceptable indoor air quality. The demand ventilation module is an apparatus adaptable to be coupled to any location on a return portion of the HVAC system and capable of drawing and regulating outside air into the HVAC system and into the inside space of a structure by way of an air pressure differential between return air and the outside air. The demand ventilation module preferably includes a damper to regulate outside air infiltration into the HVAC system and into the inside space by way of the air pressure differential between the return air and the outside air. The damper is preferably integrated into an inner chamber of a self-contained housing. The housing includes an air outlet and an outside air inlet. The housing is easily adaptable to be coupled to any location on the return portion of the HVAC system.
The demand ventilation module preferably further integrates an air restrictor plate in conjunction with the damper that defines an air-restricting opening for more accurate control of the damper under low air velocity conditions. The demand ventilation module also preferably further integrates an electronic control device configured to facilitate ventilation control, economizer operation, and HVAC unit operation. The electronic control device is capable of setting and storing pre-set minimum absolute air condition differential parameters (air condition set-points) for ventilation activation. The electronic control device is electrically connected to and controls the activation of an actuator in conjunction with inside and outside sensors that measure air conditions. Upon receiving and comparing signals from the sensors to an air condition set-point, the electronic control device can cause the actuator to automatically shift the damper to any position in the damper stroke range in direct proportion to actual real-time air condition demands (e.g., occupancy levels of the inside space as evidenced by CO2 levels).
Once installed, demand ventilation modules can also be electronically networked together into a system. This gives an operator the ability to fully control and monitor multiple HVAC units on multiple buildings at multiple sites via interfacing with the demand ventilation modules.
Thus, an advantage of this invention is that it is a universal module with adjustable damper positioning in order to accommodate various ventilation requirements subject to specific applications. Therefore, the invention is capable of retrofitting existing HVAC units and a wide variety of HVAC applications that have no or inadequate provisions for automated fresh air intake.
Another advantage of this invention is that it provides HVAC equipment with a state-of-the art computerized controls package capable of controlling, monitoring and trend logging virtually all aspects of HVAC operation, thereby providing maximum energy savings. Accordingly, the invention can provide continuous HVAC fan operation during occupied hours for continuous ventilation, while cycling the HVAC fan during unoccupied hours to save energy. The invention can also provide limitation of room temperature set-points to reduce abuse of energy and equipment, provide automatic setback temperature set-points during unoccupied hours for energy conservation, provide holiday and weekend scheduling in order to setback room temperatures or turn HVAC equipment off during unoccupied days, and provide alarms notifying building operators of conditions outside desired parameters.
Yet another advantage of this invention is that it can economize and provide xe2x80x9cfreexe2x80x9d cooling when outdoor air enthalpy, or heat content, is low enough to supplement mechanical cooling by the HVAC system.
Because the invention is completely self-contained with integral control components, it provides a simple and low cost installation, and simple and reliable quiet operation with a minimum of moving parts, thereby virtually eliminating mechanical maintenance and resulting in drastically reducing first cost and energy consumption.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of the preferred embodiment of the invention, as illustrated in the accompanying drawings.